Re: [PATCH net-next v5 00/11] net: tunnel: introduce noref xmit flows for tunnels

[Sabrina Dubroca <sd@queasysnail.net>]

2026-03-17, 12:02:30 +0100, Paolo Abeni wrote:
> On 1/13/26 5:29 PM, Marek Mietus wrote:
> > Currently, tunnel xmit flows always take a reference on the dst_entry
> > for each xmitted packet. These atomic operations are redundant in some
> > flows.
> > 
> > This patchset introduces the infrastructure required for converting
> > the tunnel xmit flows to noref, and converts them where possible.
> > 
> > These changes improve tunnel performance, since less atomic operations
> > are used.
> > 
> > There are already noref optimizations in both ipv4 and ip6.
> > (See __ip_queue_xmit, inet6_csk_xmit)
> > This patchset implements similar optimizations in ip and udp tunnels.
> > 
> > Benchmarks:
> > I used a vxlan tunnel over a pair of veth peers and measured the average
> > throughput over multiple samples.
> > 
> > I ran 100 samples on a clean build, and another 100 on a patched
> > build. Each sample ran for 120 seconds. These were my results:
> > 
> > clean:      71.95 mb/sec, stddev = 1.71
> > patched:    74.92 mb/sec, stddev = 1.35
> > 
> > TL;DR - This patchset results in a 4% improvement in throughput for
> > vxlan. It's safe to assume that we might see similar results when testing
> > other tunnels.
> 
> IMHO this performance delta is not enough to justify this amount of
> changes.
> 
> Additionally, the measured impact of removing the dst_hold/dst_release
> does not fit with my direct experience on the same matter: it should be
> below noise level in practice, as dst are per-cpu and and no
> contention/false sharing is expected in a good setup.
> 
> I think you are observing larger impact because in the veth test
> dst_release can happen on a remote CPU. Note that this setup (vxlan over
> veth) is not very relevant in practice.
> 
> I'm sorry I'm not applying this series.

This is probably fine for everybody who's been following this series,
but you answered v5 (from January) instead of v8 (posted last week).

-- 
Sabrina